The present invention relates to high pressure damage resistant decorative laminates having improved resistance to marring, abrasion, staining, dusting and crocking (as hereinafter defined), and to a method for the preparation thereof. Although not so limited, the invention is particularly applicable to laminates with textured surfaces formed either by a texture film interposed between the surface layer of the laminate and steel plates between which the laminates are subjected to heat and pressure, or from a textured steel plate. The combination of improved properties in the decorative laminate of the invention makes possible the omission of the conventional transparent surface layer, or overlay, normally required to protect the printed or pigmented decorative sheet in prior art laminates.
The novel combination of properties in the decorative laminate of this invention is achieved by coating the decorative sheet with a mixture consisting essentially of a thermoset resin, substantially fully hydrolyzed polyvinyl alcohol, fumed amorphous silica, and particulate abrasive material having a hardness higher than that of silica.
The prior art is replete with proposals for abrasion resistant decorative laminates containing finely divided mineral or abrasive materials adjacent the outermost or exposed surface thereof. To the best of applicant's knowledge, none of these prior art laminates combines improved abrasion resistance with resistance against marring, staining and crocking.
U.S. Pat. No. 4,322,468, assigned to the assignee of the present application, discloses a laminate consisting essentially of a core layer, a print layer coated with a melamine formaldehyde thermoset resin and containing finely divided abrasive materials, and a surface coating of a hydrolyzed polyvinyl alcohol-modified melamine formaldehyde having a surface coating weight of from about 40 to 140 grams per square meter, with the amount of hydrolyzed polyvinyl alcohol in the coating being from about 5 to 30% by weight of the melamine formaldehyde reaction product solids. While alleged to have improved abrasion resistance, the laminate of this patent exhibits no more than 600 cycles abrasion wear resistance by the standard NEMA test LD 3-3.01, described hereinafter.
U.S. Pat. No. 4,311,748 discloses a laminate very similar to that of U.S. Pat. No. 4,322,468, except for omission of finely divided abrasive materials.
U.S. Pat. Nos. 4,255,480; 4,263,081; 4,305,987; 4,327,141; 4,395,452; 4,400,423; 4,430,375 and 4,517,235, all assigned to Nevamar Corporation, disclose laminates and methods for the preparation thereof alleging abrasion resistant properties resulting from a thin layer (up to 0.3 mil thickness) of finely divided mineral material of 20 to 50 micron particle size and a binder. The mineral material may be silica and/or alumina, and the binder is preferably microcrystalline cellulose, with less preferred binders including anionic acrylic polymer, carboxy methylcellulose and the like. A silane may also be added as a coupling agent. The mineral particles and binder material are incorporated with a melamine formaldehyde resin or polyester resin. Typically the coating comprises about 5 to 10 parts by weight of microcrystalline cellulose for about 20 to 120 parts by weight of the mineral material. When present, a silane comprises about 0.5% to 2.0% by weight based on the weight of the mineral.
U.S. Pat. Nos. 4,499,137 and 4,532,170 disclose a laminate and a facing sheet therefor having stain and scuff resistant properties, the outer surface thereof having a thin facing layer of solid lubricant, such as a polyethylene wax, a binder and a thermosetting resin. The lubricant preferably has a particle size ranging from 1 to 25 microns and a melting point of 220.degree. to 230.degree. F. An oxidized wax or silicone resin cannot be used as a solid lubricant. The thermosetting resin may be a polyester resin or melamine formaldehyde resin. The binder is microcrystalline cellulose.
U.S. Pat. No. 4,505,974 discloses a mar-resistant decorative laminate and a method for the production thereof having a thermoset resin impregnated decorative sheet, the outermost surface thereof containing mineral particles ranging from about 5 to about 100 millimicrons in an amount ranging from about 0.5 to about 25 grams per square meter of surface area. The mineral particles are positioned within about the outermost 25 microns of the laminate. The method involves forming a thermosetting resin impregnated component sheet containing mineral particles having the size range indicated above, positioning the component sheet with its particle surface upward as the uppermost component of a decorative laminate assembly, and heat and pressure consolidating the assembly. While the laminate of this patent achieves good mar resistance, the abrasion resistance thereof is only marginally superior to that of a laminate containing no mineral particles in its outermost layer. The mineral particles are silica, alumina, titanium oxide, tin oxide, zirconium oxide, and the like.
Earlier patents disclosing the incorporation of mineral or abrasive particles in a melamine formaldehyde resin or modified melamine formaldehyde resin include U.S. Pat. Nos. 3,135,643; 3,445,327; 3,525,664; 3,798,117 and 3,975,572. None of these patents discloses laminates achieving abrasion resistance which would be considered adequate by present standards.
Despite the extensive work done in this field there is not now available a decorative laminate capable of exhibiting abrasion resistance greater than 3000 cycles ("NEMA Wear") by the NEMA test LD 3-3.01, together with superior resistance against marring, staining and crocking. A genuine need exists for such a product, particularly one having a "suede" or matte finish and a solid dark color, as well as a simplified method for production thereof using conventional equipment.